Elliptical-polarized logarithmically periodic antenna



1.961 R. H. DU HAMEL ET AL 3,013,268

ELLIPTICAL-POLARIZED LOGARITHMICALLY PERIODIC ANTENNA Filed April 23,1959 5 Sheets-Sheet 1 I N VENTDRS RAyMOND H. DpHnMEL FRED R. ORE

wwow Al I ORNENS Dec. 12, 1961 u HAMEL ETAL 3,013,268

ELLIPTICAL-POLARIZED LOGARITHMICALLY PERIODIC ANTENNA Filed April 25,1959 5 Sheets-Sheet) 2 INVENTORS Rnymouo H. DUHAMEL F-FRED R-YORE WMJMMAl I ORNEYS Dec. 12, 1961 R. H. DU HAMEL ET AL 3,013,268

ELLIPTICAL-POLARIZED LOGARITHMICALLY PERIODIC ANTENNA Filed April 2:5,1959 5 Sheets-Sheet 3 INVENTORS RAYMOND H. DuHnmEL FRED R. ORE.

r MAW ATTORN EYS This invention relates to logarithmically periodicantennas capable of operating with elliptically-polarized radiationincluding the special cases of circular-polarization andlinear-polarization at any angle.

linearly-polarized logarithmically periodic antennas havingstraight-edged teeth are described by patent application Serial Number721,408 filed March 14, 1958, by the same inventors as the presentapplication. All matter in that application relating to the constructionof logarithmically periodic antennas is incorporated herein byreference.

The present invention comprises a logarithmically periodic antennahaving at least two elements which lie in planes at right angles. Thetwo elements are constructed with the same parameter 7' which is definedin the prior-cited application. However, one of the elements isstretched with respect to the other so that their comparable teeth havedifferent distances from a common apex.

Thereore, it is an object of this invention to provide an antenna havingan elliptically-polmized radiation pattern which can be made to operateover a wide a frequency range as desired without theoreticallimitations. In practice, maximum size for an antenna structure controlsits low-frequency limit and construction tolerance controls itshigh-frequency limit. However, a 20-to-l frequency range is easilyobtainable.

It is another object of this invention to provide a frequencyindependent antenna which can be constructed to provide acircularly-polarized radiation pattern.

It is still another object of this invention to enable control of theaxial ratio of elliptical polarization.

Further objects, features and advantages of this invention will becomeapparent to one skilled in the art upon further study of the followingspecification and accompanying drawings in which:

FIGURE 1 is a perspective view of'an antenna made according to thisinvention.

FIGURE 2 shows another view of FIGURES l and 5.

FIGURES 3 and 4 illustrate transmission-line feed connections to theapex of the antenna in any of FIG- URES 1, 5, 6, 7 and 10 for oppositerotations of polarization.

FIGURE 5 shows a plane configuration of the invention and itsbi-directional patterns.

FIGURE 6 illustrates another form of the invention.

FIGURE 7 is a form of the antenna having triangular teeth.

FIGURES 8 and9 illustrate side and back views'of anelliptically-polarized antenna having two quadrature positionedelements.

FIGURES 10 and 11 show another form of elliptically-polarizedlogarithmically periodic antenna.

Certain parameters found in the prior-cited application dealing withlogarithmically periodic antennas are also applicable to the presentinvention. Theseparameters are a, B, and T, which are used to definea'single element of the antenna, designated as a half-portion in theprior application, and a parameter t defining the angle between twoelements. To summarize briefly, a is the angle bounding the sides of anelement. Angle ,8 is between a pair of rods symmetrically-placedinternally along the entire length of an element, and ,3 may be zero byusing ice a single centrally-positioned rod. Angle ,0 separates theplanes of opposite elements in an antenna. Parameter 7' controls thenumber of rods in a finite sized element and is defined by the followingexpression where R and R are the distances from the apex for comparabletransverse edges of teeth in adjacent struc- 'tural periods of anelement, where R is the larger distance. The longitudinal width of anytooth'is defined by:

Where r and R are distances from the apex of transverse edges onopposite sides of a tooth. For structural symmetry of an element:

In FIGURES l and 2, there are two pairs of antenna elements in whichelements 1% and 11 provide one pair and 12 and 13 provide a second pair.Each pair cornprises a logarithmically-periodic antenna as defined inthe above-cited patent application. However, special posi- 'tioning andrelative proportioning is necessary between factor K. To preventconfusion between the two pairs,

the apex distances for any transverse tooth'edge inpair it and 11 willbedesignated R and the apexdistance for a comparable transverse tooth'edgeimpair-12 and 13 will be designated R Comparable tooth edges "are thosehaving most nearly equal distances to-the apex.

For clarity, 'r is restated in the nomenclature distinguishing the pairsof'elements, as follows:

R, R, (4) Therefore,

R K (5) Experiments have shown the following relationship:

.h R. R..+. A r (6) where S is the time-phase in radians betweentheelectricfield vectors of the respective antenna pairs. Where-circularpolarization is desired, Sis 1r/2, and K is 7 Linear polarizationrequires S to be zero. Other values of S obtain different degrees ofelliptical polarization.

The direction of rotation of the resultantv vector of the componentquadrature electric fields is-deterrnined by the manner 'of'connectingatransmission line to the antenna.

FIGURE 3"illustrates how a transmissionline 14 may be connected to theapex portion of the antenna .toobtziin -one rotational directionofpolarization. Coaxial cable 1 14 shown in FIGURE 3 is brought-centrallyalong-antenna elementll where its outer conductoris electricallyconnected to the vertexes of elements 12 and l'ti. .The

I inner conductor is electrically connected to-the vertexes of elements13 and 11. A balanced line may be u'sedby connecting its opposite sidesin the samemanner as was done 'for the opposite sides ofthecoaxial line.

By switching the order of connections to elements-1i) and 11 as shown inFi GURE 4, the opposite direction of elliptical polarization isobtained. 7 Here, theinner' cOn- 3 ductor is connected to elements 11and 13, and the outer conductor is connected to elements 12 and 10.

The angle 4/ of each pair of elements may have any value between and180", but 1/ is preferably the same for both pairs. In the special case,where \l/ is 180, the antenna will lie along a single plane and has anedge view as shown in FIGURE FIGURE 2 is also representative of anelevational view of FIGURE 5, as well, being an end view of FIGURE 1. Inthe case of the planar arrangement of FIGURE 5, a bi-directional patternresults having radiation lobes 16 and 17.

Where it is less than 180", the radiation pattern becomesuni-directional as shown in FIGURE 1, and its predominent radiation beamis off the apex end of the antenna.

Any of the forms of teeth for logarithmically-periodic antennas may beused in the elliptically-polarized type taught by this application.Thus, in FIGURES 1 and 6, trapezoidal teeth are shown. However, inFIGURE 7, triangular teeth are provided.

The angles 11/ and on may have any value relative to each other.However, it is preferable with trapezoidal teeth that they not be closeto equality, because then the outer edges of the teeth may touch eachother to cause mutual-coupling effects which adversely affect operationof the antenna. In FIG. 1, angle 11/ is greater than angle a. In FIGURE6, angle 1/ is less than angle a. Either case is satisfactory as long asthe edges of the elements do not become too close to each other. In thecase of triangular teeth, the mutual coupling is not prohibitive whenthe angles are equal.

It has been found that the axial ratio between the magnitudes ofcomponent quadrature electric-field vectors can be maintained less than2-to-1 where circular polarization is intended over a large frequencyrange. It was also found that the ratio tended to improve as angle a wasmade smaller.

FIGURE 8 shows a side view and FIGURE 9 shows a back view of a form ofcircularly-polarized antenna having two elements 21 and 22 which arepositioned with common axes. The elements each have a pair of conductingrods 23 and 24 or 26 and 27 throughout their length and spaced by angle[3. They are electrically connected to their respective teeth.Half-portion 22 is constructed with the same value of 1- as element 21;however, element 22 is stretched by factor K defined by expression 4above. The pattern 28 of the antenna in FIGURE 8 is unidirectional asshown. This antenna is fed by connecting opposite sides of atransmission line to the vertexes of the two elements.

The frequency range of an elliptically-polarized antenna in thisapplication is determined in the same manner as was previously explainedin the above cited application. However, the tolerances for the elementsin the circularly-polarized case are generally more critical than withthe prior linear periodic antennas because of the structural phasingrelationship between the teeth of the quadrature-positioned elements,which are relatively close to each other along their sides. Furthermore,the axial ratio for the antenna tends to become more constant as angle ais decreased.

FIGURE shows a side view and FIGURE 11 illus- 'trates an end view ofanother form of the invention, which provides a unidirectional splitbeam that is elliptically polarized. It also has two pair of elements.Pair 20 and 21 comprise a split-beam nonplaner logarithmically periodicantenna as taught in a patent application titled Frequency IndependentSplit-Beam Antenna, No. 804,356, filed about April 6, 1959, by the sameinventors as the present application. The second pair of elements 22 and23 comprise a planer logarithmically-periodic antenna as taught in apatent application Ser. No. 804,357 filed about April 6, 1959, titledFrequency-Independent Unidirectional Coplaner Antenna by Hayrnond H. DuHamel and David G. Berry, and assigned to the same assignee as thepresent invention. To obtain circular polarization, the componentantennas are constructed with equal values for a and -r. The angle g forthe component coplaner antenna is made equal to the angle 1, for thecomponent non-planer antenna. Hence, elements 20 and 22 have a commonaxis, and likewise elements 21 and 23 have a common axis. One of thecomponent antennas is stretched with respect to the other componentantenna by a factor K as defined by expression 5 above, wherein S is Nlifor circular polarization.

The split-beam characteristic of the antenna in FIG URES l0 and 11 isnot obtainable with the antennas in FIGURES 1-7.

However, an antenna like the one in FIGURE 10 may be constructed to havea single forward beam by having the non-planer elements reversed to anon-image relationship, as defined in patent application Ser. No.721,408 cited above, and having the coplaner elements in an imagerelationship as defined in patent application Serial No. 804,357, filedabout April 6, 1959 by the same inventors as the present application.

One-half of the structure in FIGURES 10 and 11 is similar to theembodiment of FIGURES 8 and 9. If the one-half structure is placed overa ground plane, positioned to bisect angles 5* and it in FIGURE 10, animage of the structure will be caused in the ground plane. The one-halfstructure and its image combine to provide a structure different thanthat in FIGURES 10 and 11; because the resulting coplaner antenna has asingle beam, and the resulting nonplaner antenna has a split beam.However, the ground-plane prevents a split-beam pattern from beingobtained, and a single unidirectional beam off the apex end of theantenna results. However, their component beam patterns are differentwith equal values of a and This results in the axial ratio varying atditferent points in the beam. Accordingly, different a, all and g anglesmay be used to obtain approximate component equal patterns thatapproximately coincide; and the axial ratio is thereby madesubstantially the same over the entire beam.

Although this invention has been described with respect to particularembodiments thereof, it is not to be so limited as changes andmodifications may be made therein which are within the full intendedscope of the invention as defined by the appended claims.

We claim:

1. An elliptically polarized logarithmically periodic antenna having atleast two antenna elements, each being triangular in shape and havingapexes positioned adjacent to each other, said elements lying in planesthat are positioned perpendicular to each other, each element havingouter lateral boundaries included within an apex angle a, logitudinallyconducting means included along each element from its apex to itsopposite end, a plurality of conducting teeth formed along the edges ofeach element, vtdth, said teeth having inner and outer edges withrespect to said apexes, said teeth alternating on opposite sides of eachof said elements, the radial distances from the apex to the inner sidesof adjacent teeth on either element having a geometric-sequence ratio of-r, the ratio of the radial distance from the apex of the inner to theouter sides of a tooth being given by a geometric-sequence ratio a, oneof said elements being longer axially with respect to the other elementby a factor K, which is equal to where S represents a requiredtime-phase between quadrature electric field components.

2. An antenna as defined in claim 1 for providing circular polarizationin which S vis made T 3. An antenna as defined in claim 2 in whichlinear polarization is provided at 45 in which T is made 1 4. Anelliptically polarized antenna as defined in claim 1 in which theangular shapes of the two elements intersect each other symmetrically.

5. An elliptical-polarized logarithmicallyperiodic antenna comprisingtwo pairs of elements, each pair having two elements spaced oppositeeach other by an angular separation 0, and having adjacent apexes, onepair being positioned perpendicularly with respect to the other pair,the elements of each pair being, generally triangular in shape andhaving their ends opposite their apices positioned adjacent to eachother, each element having outer lateral bounderies included Within anapex angle a, conducting rneans connected axially along each of saidelements from its apex to its opposite end, a plurality of conductingteeth formed alternately on opposite sides of each element, said teethhaving inner and outer sides with respect to said apexes, the radialdistances from the apex of the inner sides of adjacent teeth having ageometric-sequence ratio T, the ratio of the radial distance from theapex of the inner to outer sides of a given tooth being given by ageometric-sequence ratio transmission line means having opposite sides,one of said opposite sides being connected to the apexes of one elementof each pair, and the other of said opposite sides being connected bythe other element in each pair, and one of said pair of elements havingthe radial distances of its teeth from the apex greater than theradialdistances of the teeth from the apex of the other pair of elements by anamount 6. An elliptically polarized antenna as defined in claim 5 inwhich circular polarization is provided, and one of said pairs ofelements is greater in axial proportions than the other pair by anamount 1 7. An elliptically polarized antenna as defined in claim 6 inwhich the teeth are trapezoidal in shape.

8. An antenna as defined in claim 5 in which said teeth are made ofrod-like conducting members positioned along the periphery of saidteeth.

9. An antenna as defined in claim 5 in which said teeth are triangularin shape.

10. An antenna as defined in claim 9 in which said triangular teeth areformed of rod-like conducting members positioned aiong the edges of saidteeth.

11. An antenna as defined in claim 5 in which the angle on is less thanangle 1.

12. An antenna as defined in claim 5 in which said 1/ angle is less thanangle a, said elements being interlaced with each other but notelectrically contacting each other.

13. an elliptically polarized antenna including as cornponents a firstand a second logarithmically periodic antenna, in which said antennasare positioned with a cornin-on apex, said antennas extending in thesame direction from said apex, said antennas being positioned inintersecting normal planes and being positioned over a substantiallylevel grounded surface with the apex thereof being near said groundedsurface but not touching said grounded surface, one of said antennaslying in a plane which intersects the grounded surface at an angle lessthan and which produces an intersecting line with said grounded surfacewhich is normal to the intersecting line of the normal planes in whichsaid first and second antennas lie.

14. An elliptically polarized antenna having as components a pair ofnon-planer logarithmic periodic antenna elements and a pair of co-planerlogarithmic periodic antenna elements, the two antenna elements of onepair of antenna elements each having a common center conductive boomwith separate ones of the two antenna elements of the other pair ofantenna elements, the apex of the individual antenna elements of each ofthe two pairs of antenna elements being positioned close together butnot making electrical coupling.

15. An elliptically polarized antenna in accordance with claim 14 inwhich said pair of non-planer antenna elements have an imagerelationship, and said pair of 'coplaner antenna elements have anon-image relationship, said antenna providing a radiation patternhaving a split beam with elliptical polarization.

16. An elliptically polarized antenna in accordance with claim 14, inwhich said pair of co-planer antenna elements have an imagerelationship, and said pair of nonplaner antenna elements have anon-image relationship, whereby a single predominent beam is provided ina forward direction.

References Cited in the file of this patent UNITED STATES PATENTS PetersApr. 7, 1942 Masters Aug. 30, 1949 Logarithmically Periodic AntennaArrays, by Du- Hamel and Berry, 1958 Wescon Convention Record, August1958, part I, pp. 161-174.

